Watching one of Michael Bay's deafening action movies makes you realise how Wile E Coyote felt when Road Runner succeeded in dropping a One Ton weight squarely on top of him from an enormous height. As we journalists staggered out of the press screening of Bay's latest offering, suffering from the triple-whammy of tinnitus, blurred vision and sheer resentment, we resembled a coach party outing from the local head injury clinic.

Urhhhhhh. Transformers is based, ultimately, on a toy brand from the manufacturer Hasbro. There. I've said it. A toy brand. It's not even based on a computer game. That's how fantastically de-evolved the whole sorry business is.

Anyway. A toy brand. But any sense of toy consumers - ie children, with their innocence, playfulness, imagination and charm - has been chucked overboard in favour of a boorish celebration of the film's dumbest and most reactionary demographic of 15-to-25-year-olds, to whose masturbatory needs Bay caters with passionate urgency.

Transformers are an extra-terrestrial race of beings who assume the appearance of cars or other types of hardware, but then with much whirring and clanking turn into humanoid-looking giants adorned with hi-tech looking visors in place of faces, and low-tech rusty bits of metal, nuts, bolts, plates and even untransformed car tyres all over the rest of their bodies, like genetically mutated creatures from a monster truck rally.

But it's more complicated than that: as described in the publicity material, the good ones are the Autobots®, and the bad ones are the Decepticons® - and heaven help you, incidentally, if you attempt to make free with Hasbro's trademarked names. The Decepticons® are a race of beings apparently so brazen in their evil that they have consented to have the wicked concept of deception actually enshrined in their own name! Deceiving is what the other team do as well, of course, but this dissembling is limited to the morally neutral business of suddenly pretending to be a car.

Transformers both bad and good show up on earth, and one of the good ones insinuates itself into the life of an (allegedly) likable teen dork called Sam Witwicky (Shia LaBeouf), taking the form of a beat-up old car that his grouchy dad has agreed to buy him for his 17th birthday. Instantly, the car behaves like Herbie on crack, though it does facilitate his adorably klutzy wooing of a babelicious hottie called Mikaela (Megan Fox) who is supposedly a teenager but looks like Courteney Cox Arquette's world-weary older sister.

The good transformer is here to battle the bad ones, who arrive, triggering a spectacular fire-fight with US armed forces, with tanks and armoured trucks spinning through the air and crashing noisily - and I do mean noisily - to earth. They succeed in hacking into top-secret military computers sucking super-important data out of them with astonishing speed. The Pentagon recruits a super-cool army of pulchritudinous students to help them identify these cyber-attackers.

And it is at this point that Bay boldly ventures into the field of geo-political comment. One of the students wonders if Iran could be behind it. Another snorts: "It's way too smart for Iranian scientists - what about China?" Well, naturally. On the UN Index of scientists' smartness, Iran scores pitifully low, whereas the Chinese are a right old bunch of brainiacs. I and others have written about Hollywood's continued reticence about naming America's real-world enemies. This gratuitous, nervy dismissal of "Iranian scientists" comes closer than most.

Jon Voight plays the glowering secretary of state for defence, and John Turturro is an ambiguous and thoroughly unlikable operative with a secretive government agency who attempts to push our young hero around, and is duly punished by being embarrassingly stripped down to his underwear.

And so the crash-bang story continues with eardrum-perforating explosions and detonations. The Transformers fight humans, and each other. Nobody can hear themselves think. The soundtrack is at Krakatoa levels and the editing is frenzied, almost stroboscopic, so much so that you can't really get a clear look at what the Transformers actually look like.

It's all part of the sensory-overload that the great man himself delicately calls "fucking the frame". And he has outdone himself this time. In Transformers, the director and the frame have protracted and meaningful relations, and it is over two hours before Mr Bay as it were pulls on his trousers and promises to call the frame some time next week.